Japan's Deadly Ontake Volcano Seen From Space

France's Pleiades satellite captured this image of vapor, fumes and toxic gases escaping from Ontake volcano in Japan on Sept. 30, three days after the eruption that has killed more than 54 people. This is Japan's deadliest eruption in over a century.

Despite the country's robust volcano monitoring system, this eruption came with virtually no warning. Scientists suspect this is because it was a phreatic eruption caused by steam rather than magma. When magma moves beneath a volcano, it can be picked up by seismic monitoring networks. In a phreatic eruption, ground water is superheated rapidly by the heat from magma. Because steam takes up more volume than liquid water, if enough of it is heated quickly enough with no way to escape, it can blast apart the overlying rock, pulverizing it into ash.

Japan sits on the edge of two colliding tectonic plates. The Pacific plate is being forced beneath other plates all along its border, which is known as the Ring of Fire. The ongoing collision generates earthquakes, such as the 2004 Sumatra quake that caused an Indian ocean tsunami and killed more than 200,000 people. As the Pacific plate is pushed into the Earth's mantle, surface water and hydrated minerals heat up, which in turn melts the mantle and generates the magma that causes volcanic eruptions. Japan has more than 100 active volcanoes.

The image below, captured by NASA's Aqua satellite shows Ontake the day it erupted.